Skimmed this thread and first off...OP, I'm sorry you are out money without a machine and hope you get a refund soon. He has no right to keep your money since the machine is gone and paid for by someone else.
Some of the other stuff I'm reading though ranges from nonsense to scary. I'm not going to quote anybody as I don't want to make anything personal but rather help others who may be reading this. And I speak as someone who has been buying and selling pinballs for over 15 years and ripped off many times including a MM for $10k in IN that didn't exist.
You can call it a hobby, community...whatever you want to make it seem like the pinball world is a friendly and safe haven. But the fact of the matter is that these are (now more than ever) expensive machines that -- when traded online like at Pinside, Mr. Pinball, etc. -- are traded among strangers. Just because someone posts a lot on a forum or has other people posting about him doesn't make that person safe to deal with. We're talking about individuals who may share some common interests but could have personal issues with money, health, addictions, mental stability...any combination of those and more. And for whatever reason, if someone decides to keep your money, then what? Are you going to risk going to jail over physical threats or action? Are you going to sue them when they have no money to collect? Are you going to run their name through the mud when they can just leave their name behind (change/start another Pinside name, move on from pinball, legally change name, etc.)? And please don't fool yourself into believing that the police will resolve things for you. It doesn't work like that. The sad truth to these things is that those with the least to lose are more likely to screw you over. And sometimes you get what you pay for...especially when you're chasing deals that seem too good to be true.
That said, I don't have the answer for the best/safest way to buy a pinball machine. I'm clearly biased as I turned my "hobby" into a full-time business (thanks Uncle Sam) and would suggest buying from someone like me even though so many prefer to buy only from a "collector". Clearly there is a risk in sending anyone thousands of dollars...so do your homework, respect the nature of an internet transaction, buyer beware, etc.